The present invention relates to an intake and exhaust valve system for an internal combustion engine.
Intake and exhaust valve systems commonly used in relation to internal combustion engines include rotary, sleeve and poppet valves. Of such valves, poppet valves are favoured and are predominantly in use. In typical arrangements, intake and exhaust poppet valves are separate from each other.
There is an inherent limitation in the size of separate intake and exhaust poppet valves that can be used, as such valves must open onto the top of the combustion chamber with which they are associated. There is a benefit in maximising the size of the valve openings onto the combustion chamber as this enhances the charge volume per unit time available for intake and exhaust processes, which leads to improved performance of the engine in terms of its efficiency and/or power output and which also provides improvements in the combustion process which can lead to a reduction in pollution. However, owing to their geometry, poppet valves cannot make effective use of the available area of the cylinder head. The valve openings thus provide constrictions to the flow of intake and exhaust fluids.
A further disadvantage with separate intake and exhaust poppet valves is the inherent asymmetric relationship of the poppet valves to the cylinder axis. As a result of the asymmetry, the fuel-air mixture is not introduced into the central region of the combustion chamber and so is not distributed evenly therein. Additionally, the exhaust gases do not discharge from the central area of the chamber. This asymmetry therefore limits the efficiencies at which the engine can perform the intake and exhaust processes.
With a view to alleviating the abovementioned disadvantages of separate intake and exhaust poppet valves of an internal combust ion engine, there have been various proposals to provide concentric intake and exhaust valve assemblies. Such proposals include the intake and exhaust valve systems disclosed in U.S. Pat. Nos. 4,957,073 (BERGERON), 4,449,490 (HANSEN), 5,355,848 (DENTON), and 4,893,592 (FALERO).
As identified in BERGERON, deficiencies of some of the prior proposals for concentric intake and exhaust valve systems include excessive mass associated with such arrangements, and loading problems caused by the relatively large surface area of the exhaust valve opening against compressed gases within the combustion chamber. BERGERON seeks to provide a concentric intake and exhaust valve system which provides an increased volume of charge per unit time through the engine per intake stroke and which also reduces the mass of the concentric valve assembly. Nevertheless, the intake and exhaust system proposed by BERGERON still presents a significant reciprocating mass which is undesirable.
FALERO utilises a concentric intake and exhaust valve system in which the outer intake valve has a hollow bell-shaped valve disc. The outer intake valve has a valve stem connected to the bell-shaped valve disc by radial arms, with the radial arms and the adjacent end of the valve stem being located within the confines of the bell-shaped valve disc. The bell-shaped valve disc has a generally cylindrical side wall with a flanged portion at the free end of the side wall to sealing contact with a valve seat and an inwardly curved section at the other end of the side wall. The cylindrical side wall slidingly engages an inner generally cylindrical surface defined by a somewhat annular projection positioned between the intake and exhaust ports. The annular projection co-operates with the cylindrical side wall of the bell-shaped valve disc to maintain separation between the intake and exhaust ports during movement of the outer intake valve.
FALERO does not address the problem of reciprocating mass, as is apparent from the size of the bell-shaped valve disc. Indeed, the intake and exhaust valve system proposed by FALERO utilises an arrangement in which the axial length of the side wall of the bell-shaped valve disc exceeds the axial length of the cylindrical surface on the annular projection.
There is no apparent need for the side wall of the bell-shaped valve disc to be of such length, unless the inwardly curved section at the end thereof opposed to the flanged portion is also required to seat against the annular projection when the valve is in the closed condition.
In any event, the size of the cylindrical side wall on the bell-shaped valve disc is disadvantageous in that it provides the valve with a significant reciprocating mass which is undesirable.
A further disadvantage of FALERO is location of the radial arms connecting the bell-shaped valve disc. Because the adjacent end of the valve stem is located within the confines of the hollow bell-shaped valve disc through which there is fluid flow, the presence of the valve stem can have the effect of reducing the cross-sectional flow area within the valve, so providing a restriction to flow.
A still further disadvantage of FALERO is that the annular projection forming the cylindrical surface cannot be readily refurbished or replaced in the event of excessive wear or damage.
The present invention seeks to provide an intake and exhaust valve system which has a reduced reciprocating mass in comparison to the prior art referred to above or at least provides a useful choice as an alternative to such prior art proposals. The present invention provides an intake and exhaust valve system for an internal combustion engine having a combustion chamber within a cylinder closed at one end by a cylinder head, the valve system comprising a cavity in the cylinder head opening onto the combustion chamber through a first port; a valve assembly comprising first and second valves one of which is an intake valve movable between open and closed conditions for controlling intake fluid flow into the combustion chamber and the other of which is an exhaust valve movable between open and closed conditions for controlling exhaust gas flow from the combustion chamber; the first valve comprising a valve head sealingly engagable with the first port and a skirt structure; the skirt structure being in sliding and sealing engagement with a wall structure within the cavity whereby the skirt and wall structures cooperate to divide the cavity into an inner cavity section and an outer cavity section surrounding the inner cavity section; a first flow passage communicating with the outer cavity section; and a second flow passage communicating with the inner cavity section; the second valve being disposed in the first valve for opening and closing a second port in the first valve for controlling fluid flow between the combustion chamber and inner cavity section; wherein the skirt structure has a first axial length and the tubular wall structure has a second axial length, the first axial length being less than the second axial length.
This arrangement provides a concentric intake and exhaust valve system with reduced reciprocating mass in comparison to the prior art proposals referred to hereinbefore. The reduction in reciprocating mass is accomplished by an arrangement: (a) which utilises the skirt structure (which forms part of the reciprocating mass) and the wall structure (which does not form part of the reciprocating mass) to separate the intake and exhaust gas flow paths; and (b) in which the axial length of the skirt structure is less than the axial length of the wall structure. Indeed, it is desirable to endeavour to have the axial length of the skirt structure as small as possible so as to minimise reciprocating mass, while of course maintaining an effective length having regard to factors such as height of valve lift and sealing integrity between the wall structure and the skirt structure. The skirt structure is preferably cylindrical, as is also the face of the wall structure with which the skirt structure slidingly and sealingly engages.
The skirt structure may be sealingly engagable with the wall structure by way of any suitable means such as a close sliding fit or by sealing means such as sealing rings provided therebetween.
While the wall structure may be formed integrally with the cylinder head, it is more likely to be formed either separately thereof and attached thereto in any suitable fashion, or formed in two sections one of which is integral with the cylinder head the other of which is connected to said one section.
The first valve preferably has a valve stem connected to the skirt structure. The connection between the valve stem and the skirt structure may be provided by one or more connecting elements extending therebetween. Conveniently, the or each connecting element presents a thin profile in the direction of fluid flow so as to minimise any disturbance to such flow.
Preferably, the valve stem is located outside of the confines of the skirt structure.
The first valve stem may be hollow to provide an axial passage in which the stem of the second valve is received. The second valve stem is preferably guidingly supported within the hollow first valve stem for reciprocation relative thereto.
The second valve stem may extend beyond the first valve stem.
The first valve stem and the second valve stem are preferably connected to means operable to move the first and second valves between their respective open and closed conditions in timed sequence.
A first valve biasing means such as a valve spring may be provided for biasing the first valve into the closed condition.
A second valve biasing means such as a valve spring may be provided for biasing the second valve into the closed condition.
The present invention further provides an intake and exhaust valve system for an internal combustion engine having a combustion chamber within a cylinder closed at one end by a cylinder head, the valve system comprising a cavity in the cylinder head opening onto the combustion chamber through an intake port; a valve assembly comprising an intake valve movable between open and closed conditions for controlling intake fluid flow into the combustion chamber and an exhaust valve movable between open and closed conditions for controlling exhaust gas flow from the combustion chamber; the intake valve comprising a valve head sealingly engagable with the intake port and a skirt structure; the skirt structure being in sliding and sealing engagement with a wall structure whereby the skirt and wall structures cooperate to divide the cavity into an inner cavity section and an outer cavity section surrounding the inner cavity section; an of intake flow passage communicating with the outer cavity section for delivery intake fluid thereto; and an exhaust flow passage communicating with the inner cavity section; the exhaust valve being disposed in the intake valve for opening and closing an exhaust port in the intake valve for controlling exhaust gas from the combustion chamber into the inner cavity section; wherein the skirt structure has a first axial length and the wall structure has a second axial length, the first axial length being less than the second axial length.
The present invention still further provides an intake and exhaust valve system for an internal combustion engine having a combustion chamber within a cylinder closed at one end by a cylinder head, the valve system comprising a cavity in the cylinder head opening onto the combustion chamber through an exhaust port; a valve assembly comprising an intake valve movable between open and closed conditions for controlling intake fluid flow into the combustion chamber and an exhaust valve movable between open and closed conditions for controlling exhaust gas flow from the combustion chamber; the exhaust valve comprising a valve head sealingly engagable with the exhaust port and a skirt structure; the skirt structure being in sliding and sealing engagement with a wall structure whereby the skirt and wall structures cooperate to divide the cavity into an inner cavity section and an outer cavity section surrounding the inner cavity section; an intake flow passage communicating with the inner cavity section for delivery of intake fluid thereto; and an exhaust flow passage communicating with the outer cavity section; the intake valve being disposed in the exhaust valve for opening and closing an intake port in the exhaust valve for controlling delivery of intake fluid into the combustion chamber; wherein the skirt structure has a first axial length and the wall structure has a second axial length, the first axial length being less than the second axial length.
The present invention still further provides an intake and exhaust valve system for an internal combustion engine having a combustion chamber within a cylinder closed at one end by a cylinder head, the valve system comprising a cavity in the cylinder head opening onto the combustion chamber through a first port; a valve assembly comprising first and second valves one of which is an intake valve movable between open and closed conditions for controlling intake fluid flow into the combustion chamber and the other of which is an exhaust valve movable between open and closed conditions for controlling exhaust gas flow from the combustion chamber; the first valve comprising a valve head sealingly engagable with the first port and a skirt structure; a wall structure provided in the cavity, with the wall structure or at least a section thereof being removably mounted in the cavity; the skirt structure being in sliding and sealing engagement with the wall structure within the cavity whereby the skirt and wall structures cooperate to divide the cavity into an inner cavity section and an outer cavity section surrounding the inner cavity section; a first flow passage communicating with the outer cavity section; and a second flow passage communicating with the inner cavity section; the second valve being disposed in the first valve for opening and closing a second port in the first valve for controlling fluid flow between the combustion chamber and inner cavity section.
The present invention provides an intake and exhaust valve system for an internal combustion engine having a combustion chamber within a cylinder closed at one end by a cylinder head, the valve system comprising a cavity in the cylinder head opening onto the combustion chamber through a first port; a valve assembly comprising first and second valves one of which is an intake valve movable between open and closed conditions for controlling intake fluid flow into the combustion chamber and the other of which is an exhaust valve movable between open and closed conditions for controlling exhaust gas flow from the combustion chamber; the first valve comprising a valve head sealingly engagable with the first port and a skirt structure; the skirt structure being in sliding and sealing engagement with a wall structure within the cavity whereby the skirt and wall structures cooperate to divide the cavity into an inner cavity section and an outer cavity section surrounding the inner cavity section; a first flow passage communicating with the outer cavity section; and a second flow passage communicating with the inner cavity section; the second valve being disposed in the first valve for opening and closing a second port in the first valve for controlling fluid flow between the combustion chamber and inner cavity section; the first valve having a valve stem connected to the skirt structure by at least one connecting element, said valve stem being disposed entirely outside of the confines of the skirt structure.
The present invention still further provides a cylinder head for accommodating an intake and exhaust system as previously defined, the cylinder head comprising a body having a cavity and an insert removably received in the body, the first and second valves being mounted in the insert.